Limecrete FAQs

The Limecrete FAQs aim to answer some common questions relating to Limecrete Floors.


What is Natural Hydraulic Lime (NHL)?

Natural Hydraulic Lime (NHL) is made from limestone that contains impurities such as clay and silicates. There are three European classifications: NHL 2, NHL3.5 and NHL5. The grading is determined by the compressive strength of its mortar after 28 days. Historically, NHLs were called Feeble (NHL2), Moderate (NHL3.5) and Eminently (NHL5), but the use of these terms are declining with the introduction of the European classifications.

We generally recommend the use of NHLs where the need for breathability and lower strength is outweighed by the desire for an earlier and harder set such as working on wall copings, chimneys and floors. 


Q. Which Insulation?

The preferred and improved method is to use recycled foam glass aggregate by GEOCELL. This is compressed and provides a better thermal performance, a more solid base at the most competitive price.

We also offer an insulated Light Expanded Clay Aggregate, by Techniclay for use in the original form of limecrete. Use the clay as the main insulating loose lay sub layer and as a lightweight aggregate mixed with NHL5 for the limecrete slab.


Q. What is a Geotextile Membrane?

The geotextile membrane is designed to allow moisture to move through it but it stops any larger particles or vegetation. In the Limecrete application the membrane is used to seperate the loosefill layer from the ground and then from the slab above.


Q. What is the Average Thickness of the Layers?

Glasscrete can simply be laid as compacted sub-base of GEOCELL Foam Glass at a preferred minimum depth of 150 mm. The limecrete slab is recommended to be 100 mm as this can cope with most domestic situations. Please click here for more information.


Q. What are the Drying Times?

The binder that we recommend is NHL5, it sets by an initial chemical reaction called a hydraulic set. This process gives the screed early, improved strength. The NHL then continues to carbonate over a longer period of time to reach its final compressive strength.
The temperature and humidity of the environment will affect both types of set, either by increasing or decreasing the setting process, in perfect conditions the slab will harden sufficiently to allow light movement across it within 2-3 days.


Q. Can I Install Underfloor Heating?

You can install underfloor heating when using Limecrete floors. Normally the pipes are tied to a geogrid mesh or fixed via a clip rail to the slab.
Do not use a plastic sheet system that you clip the pipes into that can seal the floor like a DPM does. Once the pipes have been fixed to the slab then you can lay a screed of NHL5 and sand over and around them, usually at 100 mm deep.

Please note that you should not use the underfloor heating for a minimum of 4 weeks after laying the screed.


Q. What Floor Finish Can I Use?

The most important factor is the moisture managing sub-base – either using foam glass of expanded clay aggregate. If this is installed to our minimum requirements, and the floor is not below ground level, then there are very few limitations as to the choice of floor finish.

For compatibility, we recommend using lime-based adhesives for bedding mortars.

As a precaution, you should install battens before laying a solid timber floor. However, engineered floors can be laid on to recommended membranes directly on to the screed.
Similarly, we recommend avoiding the use of foam underlays and foam-backed carpets to prevent any possible build-up of condensed moisture.


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